The proposed research will investigate the mechanisms involved in two different forms of experimental hypertension: oral contraceptive-induced hypertension and experimental renal hypertension. Experiments will examine the role of the renin-angiotensin system as well as the influence of sodium retention in oral contraceptive-induced hypertension. Also, these studies will examine the possibility that oral contraceptive compounds may increase the reactivity of vascular smooth muscle to pressor substances. The sodium retaining abilities of the various oral contraceptive steroids will be determined. The role of angiotensin II in the genesis of experimental renal hypertension will be investigated by the use of a competitive antagonist of angiotensin II. The time course of the hemodynamic changes that occur during the development of experimental renal hypertension in rabbits will be elucidated. Experiments will test for a possible increase in a non-renin-angiotensin pressor substance in the plasma of animals with experimental renal hypertension. Also, a study will look for possible changes in the interaction between extracellular fluid volume and plasma renin activity in animals with experimental renal hypertension.